Metallic cementation

ABSTRACT

Process for cementation of iron or steel by heat treatment in a chamber with fine particles of chromium, titanium or silicon halide suspended in an inert atmosphere.

United States Patent 1191 Kanetake 1111 3,811,929 1451 May 21, 1974 1 1METALLIC CEMENTATION [75] Inventor:

[73] Assignee: Kabushiki Kaisha Kito,

Kawasaki-shi, Kanagawa-ken, Japan [22] Filed: Mar. 2, 1971 [21]App1.No.: 120,180

Norio Kanetake, Tokyo, Japan [30] Foreign Application Priority Data2/1959 Becker et a1 117/1 19.4 X

2,901,381 8/1959 Teal 117/106 C X 2,921,877 1/1960 Samuel et a1. 117/119.4 X 2,962,388 ll/1960 Ruppert et a1. 117/106 C X 2,962,399 1l/196ORuppert et a1 148/635 3,010,856 1l/1961 Seelig et a1 1 17/1072 R X3,152,007 10/1964 Perrin et a1, ll7/l07.2 R 3,178,308 4/1965 Oxley et a11 17/1072 R 3,222,212 12/1965 Samuel et a1. 1 17/1072 R 3,325,313 6/1967Galmiche 1 17/1072 R 3,368,914 2/1968 Darnell et a1. 117/106 C X3,434,871 3/1969 Harel et a1. ll7/l07.2 R 3,573,092 3/1971 H0121 et a1l17/l07.2 R 3,684,585 8/1972 Stroup et a1. 148/635 X PrimaryExaminer-Ra1ph S. Kendall Attorney, Agent, or Firm-McGlew and Tuttle 57] ABSTRACT 5 Claims, 13 Drawing Figures INVENTOR.

FIG.

FIG.

- I Ir I 1 llll/ll/l/ l//////1/////// ll minimum 2 1 mg NORM NANE'TAKEBY MQQQM TM Pnmtiuml m4 MEIER! INVENTOR.

NO'R\ 0 KANE'TAK E PAIENTEDIAYZI Ian 3.811.929

HARDNESS (H 2'0 40 60 80 I00 DEPTH FROM SURFACE (y) FIG. 9

WEAR L085 l0 I6 [0 I6 Y) (0 1'0 1'0 NUMBER OF RECIPROCATION INVFNTOR.

Nokuo KANETAKE BY was; 'Inmu PAIENTEBIAYZI m4 FIIG.

NUMBER OF REPETITION (N) FIG. l3

0 z I. O O O 0 ll R mmOJ m m NUMBER OF TIIVES OF LIFTING (N) mvwroa MemoKiwi F K METALLIC CEMENTATION In conventional metal products, there arestainless steels, such as, high alloy steels, material requiringanticorrosion, heat-proof and wear proof properties but these metalproducts are high-priced. Therefore this invention aims at providing theabove-mentioned materials which satisfy these requirements and arelowpriced. That is to say, this invention aims at providing iron andsteel products whose exterior surface has the desired property of saidstainless and high alloy steels and whose interior has the compositionof the original material. For example, a stainless steel chain or thelike is inferior in weldability, since such a chain is made of a lowcarbon steel. This invention then is applied to this chain leaving itsinternal mechanical strength is left intact, while on the surface aloneof the chain an alloy layer having anticorrosion, heat-proof propertiesand wear proof is formed. In this way, are produced metal products, suchas iron and steel products, of low price and excellent property. Forinstance, chains can be manufactured thus.

For a better understanding of the principles of the front door 4 at thefront opening 2 is opened and then an iron and steel product 5 to betreated by cementation is moved into treatment chamber 1 through saidgas curtain supporting it by rail 6. A chromium chloride producingmaterial 7 is also moved into the treatment chamber 1.

Next, when the front door 4 is closed, the jet of a non oxidizing gasfrom the jet pipe 3 stops. After the air in the treatment chamber 1 isexhausted through an exhaust pipe 8, the temperature in the treatmentchamber is raised to about 1,000C. By this means the fine particles ofchromium chloride which are in a partly fused state throughout, or onthe circumference are floated in the treatment chamber. These particlesare maintained in that state for 5 hours and in the meantime chromium iscemented on the surface of the iron and present invention, reference ismade to the following description of a typical embodiment thereof asillustrated in the accompanying drawings, wherein:

FIG. I is a longitudinal sectional side view showing an example of ametal cementation apparatus which is used in the case of carrying outthis invention;

FIG. 2 is a longitudinal side view of the other example;

FIG. 3 is an enlarged sectional view showing a part of the normallymetallic cementation treated product;

FIG. 4 is an enlarged sectional view showing the state in which thecemented metals are partially fallen away;

FIGS. 10 to 13 show a third embodiment of this invention respectively;

FIG. 10 is a diagram showing the distribution of hardness of a chainwhichis treated by the conventional chromium cementation process;

FIG. 11 is a diagram showing the distribution of residual stress in thecase of a loaded chain;

FIG. 12 is a diagram showing results of a fatigue test; and

FIG. 13 is a diagram showing a result of the wear test.

This invention is described in greater detail "below with reference tothe aforementioned drawings.

First, anapparatus for metallic cementation of this invention isdescribed as shown in FIGS. 1 and 2. In said apparatus, anon-oxidizinggas such as nitrogen, argon or gaseous-hydrocarbon is jetted from manyjets or air holes in a jet pipe 3 installed at the lower part of a frontopening 2 of a treatment chamber 1, thus forming a gas curtain for theprevention of air invasion. A

steel product 5 and a chromium cementation zone B is formed on thesurface of a matrix A. (see FIG. 3)

Further, in the case of practical use of the invention, instead ofplacing said chromium producing material 7 in the treatment chamber 1,an opening 7' is provided in the. chamber 1 for supplying the fineparticles of metal halide. It is also possible to supply said fineparticles into the chamber 1. through the opening 7.

Next, in the treatment chamber 1 filled with a gas containing the fineparticles of said chromium chloride, a small amount of methane (0.l-5percent by volume of methane is suitable) methane is added from a feedpipe 9 and the fine particles of carbon are produced by a thermaldecomposition of methane in the treatment chamber. Chromium carbide isproduced by the reaction of these fine particles and chromium chlorideand cementation of this chromium carbide is effected on I the surfaceside of said chromium cementation zone B and thus a chromium zone C isformed on the surface of the iron and steel products in which chromiumcarbide is dispersed. (See FIG. 3) Propane gas is also useful in placeof methane gas.

Next, before the chromium cementation work is received in a coolingchamber '10 connected to the treatment chamber 1, a nonoxidizing gassuch as nitrogen, argon, hydrogen or, gaseous hydrocarbon is suppliedbeforehand to the cooling chamber 10 from a feed pipe 11. Any gascontaining iron chloride (FeCl which has escaped into the coolingchamber 10 from the treatment chamber 1 is exhausted through an exhaustpipe 12 from the cooling chamber, then the atmosphere in the coolingchamber 10 is replaced with nonoxidizing gas.

Next, an intermediate door 13 is opened between the cooling chamber 10filled with nonoxidizing gas and the treatment chamber 1,and'the-chromium cemented iron and'steel product is moved into thecooling chamber 10 supported by the rail 6 as indicated by referencenumeral 5. Thereafter, the intermediate door 13 is closed and cooling ofthe chromium cemented iron and steel product takes place in the coolingchamber 10. Then, nonoxidizing gas is emitted from the jet pipe 3 of thefront opening 2. As a result a gas curtain is formed 3 and the frontdoor 4 is opened and a second iron and steel product to be treated bychromium cementation is moved into the treatment chamber 1 as in theaforesaid case preventing air invasion .into the treatment chamber 1 bythe air curtain. Then a chromium cementation takes place as in theaforesaid case.

Next, when the chromium cemented iron and steel product in the coolingchamber is cooled below about 300C, nonoxidizing gas is emitted from ajet pipe located at the lower part of a rear opening 14 of the coolingchamber 10. As a result a gas curtain is formed and then a front door 16is opened. The chromium cemented iron and steel product is taken out theinside of the cooling chamber 10 and air-cooled up to room temperature.The air invasion into the cooling chamber 1 is prevented by the gascurtain.

As shown in FIG. 3, the structure of section of a the chromium cementediron and steel product obtained as described above, there are formed,the chromium cementation zone B and the chromium zone C in whichchromium carbide is dispersed. These zones B and C are formed in turn onthe surface of the matrix A of ferrite and pearlite structures as shownin FIG. 3. The chromium cemented iron and steel product is cooled up toa certain temperature in the cooling chamber without the bad influenceof an atmosphere containing iron chloride (Fe C1 produced in thetreatment chamber by saidchromium cementation. For this reason nodechromium phenomenon takes place such astakes place in the case ofcooling in an atmosphere containing iron chloride (FeCl Therefore'thechromium cemented iron and steel product treated by the process of theinvention is rich in brightness.

Further as shown in FIG. 2, a quenching chamber 18 having an oil tank 17is provided instead of the cooling chamber 10 and the atmosphere ofnonoxidizing gas is produced in the treatment chamber 1. Then, thechromium cemented iron and steel product is moved from the treatmentchamber I to the quenching chamber 18 and is directly thrown into theoil tank 17 where quenching in oil takes place. The section structure ofthe chromium c'ementated iron and steel product is obtained by making atempering successively within the limits of l80-600."C. The chromiumcementation zone and the chromium zone in which chromium carbide isdispersed, are formed in turn on surface of the matrix of the steelproducts tempered martensite structure yielding a chromium cemented ironand steel product which is rich in brightness without causing adechromium phenomenon.

Further, in carrying out this invention, a curtain of the nonoxidizinggas may be provided instead of intermediate door 13. After chromiumcementation takes place in the treatment chamber 1, the chromiumcementation treated work may be moved directly to the cooling chamber 10or the quenching chamber 18, omitting the supply of methane andnonoxidizing gas into the treatmentchamber 1. Chromium iodide orchromium fluoride or the like may be used as chromium halide besideschromium chloride. Further, the,

same result can be obtained even by the use of titanium halide, forinstance, titanium chloride (TiCl or silicon halide (SiCl4), instead ofchromium halide.

As a means of producing the atmosphere of said halide in the treatmentchamber, the material producing halide may be placed beforehand in thetreatment chamber as mentioned above. Thereafter, the fine particles ofhalide are supplied into the treatment chamber 1 from the feed pipe 9.Alternatively those means may concurrentlybe used.

In a further embodiment of the invention the front part of the treatmentchamber is provided with a gas jet pipe 19 for forming a gas curtain anda preheat chamber 21 having a front door 20. When cementation ofanticorrosion metal into the desired iron and steel products is takingplace in the treatment chamber 1, other iron and steel products can bepreheated in the preheat chamber 21 whereby cementation of anticorrosionmetal can more efficiently take place.

The following description is set forth below with reference to variousembodiments of this invention:

Embodiment l-(A) Under the following conditions, there was made achromium cementation in the gear for a chemical machine made of carbonsteel containing a chemical composition of C 0.025 percent, Si 0.25percent, Mn 0.8 percent, P 0.011 percent and S 0.025 percent.

1. Treatment Amount: I50 Kg (70 pieces) per one time 2. CementationTemperature: l,000C

3. Cementation Time: 5 hours 4. Cooling Time in Cooling Chamber: 2 hours(aircooled in the atmosphere. after the cooling in the cooling chamber)The chromium cementation work obtained had a chromium zone of 18p.thickness and was rich in brightness without causing a dechromiumphenomenon as shown in FIG. 4. Results were also good as regardscorrosion resistance in nitric acid solution.

Embodiment l-( B) Under the following conditions, there was made achromium cementation in a gear made of chromiummolybdenum steelcontaining-a chemical composition of C 0.4 percent, Si 0.32 percent, Mn0.82 percent, P 0.021 percent, S 0.015 percent, Cr 1.02 percent and Mo0.25 percent. I

1. Treatment Amount: 150 Kg (15 pieces) per one time 2. CementationTemperature: 1,030C

3. Cementation Time: 5 hours 4. Oil quenching takes place immediatelyafter the cementation.

The chromium cementation work thus obtained had a chromium zone of 20p.thickness and wasrich in brightness without causing a dechromiumphenomenon as shown in FIG. 4. The resultant workhad an HRC (Rochwellhardness) in surface hardness of and HRC 52in core hardness. As a resultthis gear was remarkably improved in resistance to corrosion and wear ascompared with the ordinary work.

Embodiment 2 m) 1. Specimen: I A surface smooth round bar of 9.5 mm dia.and 50 mm long having the following chemical composition was treated: II

Chemical Composition of Specimen 2. Treatment a In to a furnace whoseinterior atmospheric gas can be controlled from the outside, specimensand chromium chloride producing material are placed after removing theair inside the furnace, fine particles of chromium chloride (CrCl whichare in a partially fusing state throughout or on the circumference inthe furnace are generated by raising the temperature in the furnace toabout 1,000C. That state is maintained for about 5 hours while in themeantime cementation of chromium is effected on the surface of eachspecimen in the furnace. Thereupon a chromium cementation zone is formedon said specimens. Then in the furnace filled with the gas containingthe fine particles of said chromium chloride, a small amount of methaneis added and fine particles of carbon are produced by the thermaldecomposition of methane in the furnace. By the reaction of these fineparticles of carbon and chromium chloride, chromium carbide is produced.Then, a chromium zone in which chromium carbide is dispersed was formedon the surface of the specimen by the cementation of this chromiumcarbide on the surface side of said chromium cementation zone. In theforegoing, a volume ratio of 0. 1-5 percent of methane to gas issuitable. Also, propane gas may be used in place of methane.

Next, that specimen is cooled in oil immediately after removal from saidfurnace and quenching is performed preventing oxidation on the surfaceof the specimen. Tempering is performed within the limits of l80-600Ccorresponding to the mechanical property successively being required.

As shown in F IG. 5, in, the structure sectional of surface treated,specimen I obtained as described, there were formed (i) a chromiumcementation zone B of about a in average thickness and (ii) a chromiumzone C of about p. in average thickness in which chromium carbideisdispersed, in turn on the surface of matrix A of the temperedmartensite structure.

3. Treatment b:

As shown in FIG. 6, the completion of the foresaid chromium carbidecementation, in another embodiment the specimen is slowly cooled in thefurnace omitting the oil quenching in the structure of the surfacetreated specimen ll. On the surface of the steel product matrix offerrite and pearlighte structure (ii) a chromium zone B of 15a inaverage thickness and (ii) a chromium zone C of 20p. in averagethickness in which chromium carbide is dispersed.

4. Specimen by the conventional treatment:

As shown in FIG. 7, after treatment was made at 1,000C for 5 hours bythe conventional chromium cementation process, there were formed in turnon the surface of matrix A of ferrite and pearlite structure in thesurface section structure of treated specimen lll obtained by the slowcooling of the specimen in the furnace, (i) a decarburizing zone D offerrite structure of 10 in average thickness, and (ii) a chromiumdiffusing zone E of 5p. in average thickness and (iii) chromium zone Fof 20p. in average thickness.

5. Wear Test: I

Two pieces each of said specimens 1, ll, ill are arranged at rightangles to each other as shown in-FlG. 8 and machine oil is applied aslubricant to said pieces, which are subjected to a load of 500 Kg andreciprocated. In this manner an amount of change in diametersize wasmeasured to indicate wear loss.

As the result, as compared with a wear resistance of the surface ofspecimen Ill treated by the conventional chromium cementation process,the wear resistance is excellent proof of the surface of specimen lltreated by process of this invention slowly cooled in the furnace. Thewear resistance of the surface of specimen 1 treated according to theprocess of this invention by quenching and tempering is much moreexcellent. These results are seen in FIG. 9.

Embodiment 2-(B) l. Specimen:

The specimen is the same as in the case of Embodiment 2(A).

'2. Treatment:

Each specimen in this example was treated under the same conditions asdescribed in Embodiment 2-(A) above. After the chromium cementation zonewas formed, a small amount of carbon powder in form of fine particles ofcarbon of a very small diameter is added in the furnace. Then, chromiumcarbide is produced by the reaction of chromium chloride and carbon, andcementation and dispersion of this chromium carbide were performed inthe chromium zone. Thereafter, the specimen was manufactured whosequenching and tempering-took 'place under the same conditions as inEmbodiment 2-(A) above and the specimen was manufactured whose slowcooling was performed inthe furnace. in this example, about 10 to 4Embodiment 2-(C) l. Specimen:

The specimen in this example is the same as the specimen described inEmbodiment 2-(A).

2. Treatment: a

Cementation was performed beforehand in each of said specimen and acementation zone of 0.03-1 .5 mm thickness was formed in the specimens.The resultant specimen and a chromium chloride producing material areplaced in the furnace. After the removal of air from the atmosphere inthe furnace, the temperature is raised by heating and is maintained at1,000C for 5 hours and chromium cementation takes place. Next, thequenching and tempering of the specimen was performed under the sameconditions as in the example of Embodiment 2--(A) and the specimen whoseslow cooling was performed in the furnace, were manufactured.

In the surface treated specimen so obtained, a cementation zone and achromium zone in which chromium carbide is dispersed, were formed inturn on the surface of the iron and steel matrix and said speciman hadthe same wear resistanceas described in example of Embodiment 2-(A).

Further, in the case of Embodiment 2--(C), even if a carbonitridingtreatment is performed instead of cementation, the same result isobtained. The iron and steel product whose surface treatment isperformed by the process of this invention, forms a chromium zone on itssurface, so that a rust by corrosion is not produced in the atmosphereas for corrosion resistance to fresh water, sea water, nitric acid,organic acid or the like, this corrosion resistance can be remarkablyimproved. This is so, since in the chromium zone there exist super hardcrystals consisting of chromium and titanium carbide or nitride in thestate of dispersion, a wear resistance can be remarkably improved.Further chromium is sufficiently diffused in iron and a metal phase isassumed, so that even if a heavy load partially acts on the so treatediron product, the chromium zone can securely be prevented from itscoming off and the iron and steel matrix is made into a temperedmartensite structure by quenching and tempering. Therefore, these arethe results the iron product increases in a breaking strength,andsufficiently endures a contact pressure and shows further improvedwear resistance.

Embodiment 3 cementation zone B (chromium iron alloy layer) of about17;:- in average thickness and a chromium zone C of about 24% in averagethickness in which chrmium carbide is dispersed, are formed in turn ,onthe circumference of core A of a tempered martensite structure byquenching and tempering. As shown in FIG. 10, and in the distribution ofhardness of its section, a hardness of the chromium zone C is thehighest,

. also tested and results given below:

the link chains, as shown in FIGS. 3 and 5, a chromium while thechromiumcementation zone B has a hardness of iron chromium alloystructure and the core has a tempered martensite structure which is highin hardness.

And as mentioned above, when quenching and tempering are performed afterthe chromium cementation, in the section structure of the link chain,its specific volume varies according to the difference of transformationin each of the chromium zone C, the chromium cementation zone B and thecore A. Thus, as shown in FIG. 11, a residual stress (compression) isproduced on the surface side of the rod and a residual stress (tension)is produced on the center side of the rod. On this account, a pre-stress(compression) is given within the straight portion 5 of the link chainand improvement of I a fatigue strength was seen.

Next, description is made below. with regard to the results of testingthe link chain of this invention. The conventional link chain in whichchromium cementation is not performed, is also tested and results givenbelow. The link chain manufactured by the treatment of the conventionalchromium cementation process is 1. Fatigue Test:

A conventional link chain I of 7.1 mm in normal size and 20.2 mm inpitch consisting of low manganese steel having a chemical composition ofC 0.23 percent, Si 0.21- percent, Mn 1.43 percent, P 0.012 percent and S0.023 percentis tested. Also, a link chain 11 (about 24p. in averagethickness of chromium zone C, about 17p. in average thickness ofchromium cementation zone) according to this invention is obtained byperforming chromium cementation and heat-treatment for said conventionallink chain by the process of said Embodition of C 0.23 percent, Si 0.21percent, Mn 1.43 'percent, P 0.012 percent and S 0.023 percent. Adecarburizing zone of ferrite structure, a chromium diffusing zone and achromium zone were formed in turn on the circumference of the coreconsisting of ferrite and pearlite. The average thickness of each zoneis 9 z 48p, 10 z 17p. and 11 24p. respectively.

B Specimen II:

The chromium cementation described in the Embodiment was performed forsaid link chain. As shown in FIGS. 3 and 5, a chromium cementation zoneB and a chromiumzone C in which chromium carbide is dispersed, wereformed in turn on the circumferenceof the core A of tempered martensitestructure by quenching and tempering. The average thickness of each zoneis 13 -17 and 14 24 respectively.

When said specimens I and II, were tested for a wear resistance, theresults shown in FIG. 13 were obtained.

Further, in the wear proof test, machine oil was applied to the linkchain and a load of 1 ton was given to the link chain and its going upand down was repeated.

As a result, a wear loss was measured (difference between the pitchafter test and the pitch before test).

Since the link chain treated according to this invention forms achromium zone on its surface, corrosion 1 by rust is not produced intheatmosphere. Corrosion resistance to fresh water, sea water, nitricacid, organic acid or the like, can be remarkably improved for thischain. Also, in itschromium zone, super hard crystals consisting ofcarbide or nitride of chromiums and titaniums, exist in the state ofdispersion so that wear resistance'can be remarkably improved and thecore has a tempered martensite structure-by quenching'and tempering.Therefore breaking strength can be increased and when the link chain issubjected to load, there is sufficient endurance against a contactpressure in the mutual contact portion of links. Further,.as is clearfrom the metal structure and the hardness distribution shown by FIG. 10,the chromium in'the steel is sufficiently diffused and assumes an alloyphase. Also harding said halide suspended as fine particles in an inertatmosphere in said chamber while maintaining the same mainly in apartially fused state whereby the so-- coated work is protected againstcorrosion, heat and/or wear.

2. Process of metallic cementation of a work, which comprises performingsaid metallic cementation by coating the work composed of iron or steelheated to cementation temperature in a treatment chamber with volatilemetallic halide selected from the group consisting of halides ofchromium, titanium and silicon, maintaining said halide suspended asfine particles in an inert atmosphere mainly in a partially fused state,and cooling the so-cemented work in a cooling chamber containing anon-oxidizing gas in which-by-products comprising iron halide areremoved, whereby said work so coated is protected against corrosion,heat and wear.

' maintaining said halide suspended as fine-particles in an inertatmosphere mainly in a partially fused state, and successively quenchingthe so-cemented work and successively utilizing for the quenching theheat produced by the treatment at the required quenching temperature of180 600C, said quenching being performed in a quenching chambercontaining a nonoxidizing gas in which by-products comprising ironhalide are removed, whereby said work so coated is protected againstcorrosion, heat and wear.

4. Process for surface treatment of iron and steel products, whichcomprises treating and coating the iron and steel products heated tocementation temperature in an inert atmosphere with fine particles ofmetallic halide selected from the group consisting of chromium, titaniumand silicon halides, said particles being suspended in a partially fusedstate, and forming a metallic diffusing zone on the surface of said ironand steel products matrix, and then adding fine particles of carbon to,said atmosphere, whereby a carbide of said metal is dispersed on thesurface of said diffusing zone and said product is protected againstcorrosion, heat and wear.

5. Process for surface treatment of iron and steel products, whichcomprises coating said products heated to cementation temperature byforming a carburizing zone or a carbonitriding zone on the surface ofsaid iron and steel products matrix by carburizing or carbonitriding theiron and steel products beforehand, and then treating those iron andsteel products in an inert atmosphere with fine particles of metallichalide, said particles being suspended and being selected from the groupconsisting of chromium, titanium, and silicon, whereby said particlesimpart to said products corrosion resistance, heat resistance, and/orwear resistan'ce, and are suspended mainly in a partially fused state,whereby said metal is cemented on the surface of said carburizing zone.or carbonitrizing zone and the metallic carbide is dispersed on thesurface of a diffusing zone. l

2. Process of metallic cementation of a work, which comprises performingsaid metallic cementation by coating the work composed of iron or steelheated to cementation temperature in a treatment chamber with volatilemetallic halide selected from the group consisting of halides ofchromium, titanium and silicon, maintaining said halide suspended asfine particles in an inert atmosphere mainly in a partially fused state,and cooling the so-cemented work in a cooling chamber containing anon-oxidizing gas in which by-products comprising iron halide areremoved, whereby said work so coated is protected against corrosion,heat and wear.
 3. Process of metallic cementation of a work, whichcomprises performing said metallic cementation by coating the workcomposed of iron or steel heated to cementation temperature in atreatment chamber with volatile metallic halide selected from the groupconsisting of halides of chromium, titanium, and silicon, andmaintaining said halide suspended as fine particles in an inertatmosphere mainly in a partially fused state, and successively quenchingthe so-cemented work and successively utilizing for the quenching theheat produced by the treatment at the required quenching temperature of180* - 600*C, said quenching being performed in a quenching chambercontaining a non-oxidizing gas in which by-products comprising ironhalide are removed, whereby said work so coated is protected againstcorrosion, heat and wear.
 4. Process for surface treatment of iron andsteel products, which comprises treating and coating the iron and steelproducts heated to cementation temperature in an inert atmosphere withfine particles of metallic halide selected from the group consisting ofchromium, titanium and silicon halides, said particles being suspendedin a partially fused state, and forming a metallic diffusing zone on thesurface of said iron and steel products'' matrix, and then adding fineparticles of carbon to said atmosphere, whereby a carbide of said metalis dispersed on the surface of said diffusing zone and said product isprotected against corrosion, heat and wear.
 5. Process for surfacetreatment of iron and steel products, which comprises coating saidproducts heated to cementation temperature by forming a carburizing zoneor a carbonitriding zone on the surface of said iron and steelproducts'' matrix by carburizing or carbonitriding the iron and steelproducts beforehand, and then treating those iron and steel products inan inert atmosphere with fine particles of metallic halide, saidparticles being suspended and being selected from the group consistingof chromium, titanium, and silicon, whereby said particles impart tosaid products corrosion resistance, heat resistance, and/or wearresistance, and are suspended mainly in a partially fused state, wherebysaid metal is cemented on the surface of said carburizing zone orcarbonitrizing zone and the metallic carbide is dispersed on the surfaceof a diffusing zone.